A widely used class of impression materials are alginates. Alginates consist of derivatives of alginic acid which, after stirring with water, cure in a sol-gel process. Typically, these impressions are made as so-called one-phase or monophase impressions, i.e. only a single viscosity of the impression material is employed when taking the impression. Alginate impression materials are also generally cheaper than many other impressions materials, such as vinyl polysiloxane (VPS) impression materials. Alginates are often used for study models, as a matrix for temporary crown and bridge materials, and for making orthodontic impressions. Due to their low tensile strength and elongation at break values, they are usually easy to cut or trim. This can be an advantage for some applications, e.g. in the orthodontic field. For example, materials with a comparable low tensile strength can facilitate making impressions over brackets of a patient receiving an orthodontic treatment without causing the risk of pulling off the brackets during removal of the set impression due to the low tear resistance at these spots.
Due to these features, alginates are often the material of choice for specific impressioning applications.
However, cured alginate impression materials typically lack dimensional stability due to loss of water and cannot be stored over a long period of time without degradation.
Also, for impressions that are used as a matrix for temporary crown and bridge (C&B) materials, it may be desirable for the material to have a low elongation-potential, that is, low elasticity. Generally, alginates are not very elastic.
Alginate impression materials are also sometimes cumbersome to be used. They have to be prepared freshly by mixing an alginate powder with water. Thus, they cannot be provided in ready-to-use foil bags.
Therefore specially designed VPS impression materials have been developed trying to mimic the properties of alginates but trying to keep the advantage of high dimensional stability of VPS impression materials combined with the ability to mix them in automatic mixing systems (Garant™ or Pentamix™; 3M ESPE). An example of such a dental composition is given in U.S. Pat. No. 6,121,362.
These materials are quite successful in the market (Position™, 3M ESPE), but they still show properties which are not identical to alginates, e.g. with regard to tensile strength and elongation at break.
A reduction of the physical strength of the set VPS material cannot be easily reached without jeopardizing other feature like curing speed, elastic recovery or shore hardness or prize.
Thus, there is a need for a substitute or alternative for alginate containing impression materials. There might also be a need for reducing efforts in the production process, packaging process or storage process.
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